Techniques are described herein for returning a repository to a prior
state. The repository may be, for example a database, and the prior state
may be, for example the consistent state that the database had at a
particular point in time in the past. When a operator-caused error has
been introduced to the database by changes made by an already-committed
transaction, the techniques described herein may be used to recover from
the error by returning the database to a point in time prior to the
commit time of the transaction that introduced the error. The techniques
involve the generation of "physical undo" information, and the use of the
physical undo information in conjunction with physiological undo and
physiological redo to efficiently return a repository to the prior state.